You left the 220/115v plug and used it to charge the battery. It is a safety problem - someone can plug through it the battery to the 220/115 volt and blow the battery! Please destroy the plug or make it unusual.

whenever I need a charger, switching power supply, or the like, I can usually find one at my local Habitat for Humanity store for next to nothing. Everything from 3v to 24v has been there at least once.

I didn't, just because I already had a "wall-wort"-style charger that is already exactly the right charger for this battery. However, I really LIKE the idea of having an integrated charger, just because it would be so cool just to run the power cord right from the wall into the power supply.